Shielded common return pairs and coaxial cable



June 6, 1967 o. G. GARNER SHIELDED COMMON RETURN PAIRS AND COAX IAL CABLE Filed March 25, 1965 LOW FREQUENCY SIGNALING APPARATUS I3 24 LOAD HIGH FREQUENCY A SIGNALING APPARATUS INVENTOR QSCAR G. GARNER HIGH FREQUENCY SIGNALING APPARATUS BY 21% fine; I

ATTORNEYS. I

United States Patent SHIELDED CUMMON RET COAXIAL CABLE Oscar G. Garner, Westiieid, N.J., assignor to General Cable Corporation, New York, N.Y., a corporation of New Jersey Filed Mar. 25, 1965, Ser. No. 442,745 6 Claims. (Cl. 333-1) PAIRS AND ABSTRACT OF THE DISCLOSURE This invention relates to cables and more particularly to a cable designed to permit simultaneous transmission of radio-frequency, very high frequency, and ultra-high frequency signals and voice, carrier, pulse or power signals.

One object of the invention is to provide a cable in which a center conductor of a coaxial cable provides a common return for one or more insulated single conductors located between the center conductor and the sheath of the coaxial cable.

Another object is to provide a sheath or shield over all of the cable pairs and to use this sheath as the outer conductor for a coaxial cable.

It is a further object to provide a composite construction for a cable in which a normal coaxial pair and common return pairs make use of the same metal and geometry thus effecting an economical cable with no sacrifice of transmission quality.

The invention provides a shielded electrical cable particularly suitable for common ground return transmission of either communication or power frequency energy. The cable includes a pair or pairs of spaced conductor wires and a common center conductor is provided as one wire in each of the pairs. The center conductor is insulated with a suitable insulation such as a multi-cellular dielectric or solid dielectric over which are applied signal conductors laid either straight, spiral or twisted and with the whole shielded and enclosed in a metallic sheath.

The common return pair or pairs may be employed as voice frequency, pulse, carrier or power transmission lines and the coaxial pair comprising the common center conductor and the shield may be employed at the same time for radio-frequency, very high frequency and ultra-high frequency signal transmission. The shielded multi-conductor cable having a pair or pairs with a common center conductor return and a coaxial cable employing the common center conductor as its inner conductor, may be employed in the same way as power or communication transmission lines with earth return while at the same time employed as a normal high frequency coaxial transmission line.

Further objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views FIGURE 1 is an enlarged, fragmentary, isometric view showing the cable of this invention with parts broken away to show the interior construction;

a modified form of the invention;

FIGURE 4 is a fragmentary side elevation, partly in section and partly broken away, showing a modified form of sheath from that disclosed in FIGURE 1; and

FIGURE 5 is a diagrammatic view illustrating the way in which the cable of FIGURE 1 is used for carrying low frequency and high frequency signals at the same time.

FIGURE 1 shows a cable 10 with an outer metallic sheath 11 which is smooth in the illustrated construction and which serves as the outer conductor for the coaxial part of the invention. The sheath 11 is preferably made of copper or aluminum, but it may be made of other kinds of metal.

Electrical insulation 12 constitutes a coating of enamel or an extrusion of a somewhat flexible synthetic or rubberlike material of suitable dielectric properties around a conductor 13. Polyethylene or polyester resin may be used for the insulation coating 12.

FIGURES 1 and 2 show a single insulated conductor 13 in the cable 10, but FIGURE 3 shows a modified cable 10'. Parts of the cable that are the same as in FIGURE 2 are indicated by the same reference characters. The cable 10 includes a plurality of insulated conductors 13. Each of the conductors 13 is preferably made of copper or aluminum wire, e.g. No. 28 or 38 or 44. These sizes are given merely by way of illustration.

The insulated conductors 13 are at least partially embedded in other insulation 14 which surrounds the center conductor 16 that is coaxial with the sheath 11. The insulation 14 preferably fills the space between the center conductor 16 and the outer sheath 11. In the illustrated construction, the separate conductors 13 are fully embedded in the insulation 14. This insulation 14 can be made of an extrusion of multi-cellulose polyethylene or any flexible synthetic or rubber-like material of suitable dielectric properties. The center conductor 16 is cylindrical and is of larger cross-section than the separate conductors 13. No. 12 copper or aluminum wire is suitable for the center conductor 16, but this size is also given merely by way of illustration. 1

FIGURE 4 shows the same construction as in FIGURES 1 and 2 but with a corrugated sheath 20 of a minimum inside diameter substantially equal to the outside diameter of the insulation 14. It is not necessary for the insulation 14 to extend into the convolutions of the sheath 20. The corrugations of the sheath 20 are generally circumferential, but a single pitch helix is preferable for more continuous manufacture, though the invention can be made with convolutions which are entirely circumferential.

FIGURE 5 shows a way in which the cable of this invention is used to transmit low frequency and high frequency signals simultaneously. The sheath 11 is connected into a high frequency circuit by conductors designated 21. This circuit includes the center conductor 16 through a capacitor 22 and an impedance 24. The capacitor 22 acts as a high pass filter which blocks low frequency signals from entering the high frequency circuit 21.

The transformer 26 is connected between the conductor 13 and the common return or center conductor 16. This transformer 26 acts as a low pass filter which chokes oif high frequency signals but the low frequency current passes easily through the transformer.

The common return pairs are terminated at their characteristic impedance by way of transformers 26 and the coaxial conductor is terminated at its characteristic impedance 24. The duplexing of the low frequency information from the high frequency information is thus accomplished by the frequency filtering action of the transformers 26 and the capacitors 22.

The preferred embodiments of the invention have been limited and described, but changes and modifications can be made and some features can 'be used in different combinations without departing from the invention as defined in the claims.

What is claimed is:

1. An electric communication cable for simultaneously transmitting high frequency signal currents and low frequency signal currents comprising, in combination, a centrally disposed common-return conductor, an extruded wall of insulation surrounding the centrally disposed common-return conductor, a further conductor insulated with a relatively thin Wall of insulation longitudinally coextensive with the centrally disposed common-return conductor and disposed at the outer surface of the extruded wall of insulation surrounding the centrally disposed comanon-return conductor, and an outer conductor comprising a continuous metallic sheath enclosing the said insulated conductors, the centrally disposed common-return conductor and the outer conductor constituting a circuit for the transmission of high frequency signal currents, and the centrally disposed common-return conductor and the said further conductor constituting a circuit for the simultaneous transmission of low frequency signal currents.

2. A coaxial cable for the simultaneous independent transmission of high frequency and low frequency signal currents and in which the high frequency circuit comprises an inner conductor and an outer conductor in the form. of a continuous metallic sheath enclosing the inner conductor, and a wall of insulation surrounding the inner conductor spacing the outer conductor substantially concentrically with respect to the inner conductor, and in which the low frequency circuit comprises the said inner conductor and a further conductor longitudinally co-extensive with the inner and outer conductors, the said fur- 4. ther conductor having a relatively thin coating of insulation thereon, the said insulated further conductor being disposed within the outer conductor near the periphery of the wall of insulation which spaces the inner and outer conductors from each other.

3. The cable described in claim 2 characterized by there being a plurality of the further insulated conductors disposed within the outer conductor near the periphery of the wall of insulation which spaces the inner and outer conductors from each other, each of said further conductors constituting with the inner conductor an independent circuit for the transmission of low frequency signal cur rents.

4. The cable described in claim 2 characterized by the further conductor being embedded in the outer surface of the Wall of insulation which spaces the inner and outer conductors from each other.

5. The cable described in claim 2 characterized by the outer conductor being corrugated with the ridges of the corrugations extending generally circumferentially around the cable.

6. The cable described in claim 2 in combination with capacitor means connected in the high frequency circuit for preventing the flow therein of low frequency currents, and transformer means connected in the low frequency circuit for preventing the flow therein of high frequency currents.

References Cited UNITED STATES PATENTS 2,048,091 7/1936 Aifel et al. 333* X 2,227,384 12/1940 Wiessner 333-70 X 2,235,018 3/1941 Hagen 33370 X 3,082,387 3/1963 Monelli et al. 333-84 X 3,173,990 3/1965 Lamons l74l0 2 HERMAN KARL SAALBACH, Primary Examiner.

M. NUSSBAUM, Assistant Examiner. 

1. AN ELECTRIC COMMUNICATION CABLE FOR SIMULTANEOUSLY TRANSMITTING HIGH FREQUENCY SIGNAL CURRENTS AND LOW FREQUENCY SIGNAL CURRENTS COMPRISING, IN COMBINATION, A CENTRALLY DISPOSED COMMON-RETURN CONDUCTOR, AN EXTRUDED WALL OF INSULATION SURROUNDING THE CENTRALLY DISPOSED COMMON-RETURN CONDUCTOR, A FURTHER CONDUCTOR INSULATED WITH A RELATIVELY THIN WALL OF INSULATION LONGITUDINALLY COEXTENSIVE WITH THE CENTRALLY DISPOSED COMMON-RETURN CONDUCTOR AND DISPOSED AT THE OUTER SURFACE OF THE EXTRUDED WALL OF INSULATION SURROUNDING THE CENTRALLY DISPOSED COMMON-RETURN CONDUCTOR, AND AN OUTER CONDUCTOR COMPRISING A CONTINUOUS METALLIC SHEATH ENCLOSING THE SAID INSULATED CONDUCTORS, THE CENTRALLY DISPOSED COMMON-RETURN CONDUCTOR AND THE OUTER CONDUCTOR CONSTITUTING A CIRCUIT FOR THE TRANSMISSION OF HIGH FREQUENCY SIGNAL CURRENTS, AND THE CENTRALLY DISPOSED COMMON-RETURN CONDUCTOR AND THE SAID FURTHER CONDUCTOR CONSTITUTING A CIRCUIT FOR THE SIMULTANEOUS TRANSMISSION OF LOW FREQUENCY SIGNAL CURRENTS. 